Level shifts in a panel data based unit root test. An application to the rate of unemployment

Several unit root tests in panel data have recently been proposed. The test developed by Harris and Tzavalis (1999 JoE) performs particularly well when the time dimension is moderate in relation to the cross-section dimension. However, in common with the traditional tests designed for the unidimensional case, it was found to perform poorly when there is a structural break in the time series under the alternative. Here we derive the asymptotic distribution of the test allowing for a shift in the mean, and assess the small sample performance. We apply this new test to show how the hypothesis of (perfect) hysteresis in Spanish unemployment is rejected in favour of the alternative of the natural unemployment rate, when the possibility of a change in the latter is considered.structural breaks, unit roots, panel data, unemployment

Breaking the panels. An application to the GDP per capita

This paper proposes a test statistic for the null hypothesis of panel stationarity that allows for the presence of multiple structural breaks. Two different specications are considered depending on the structural breaks affecting the individual effects and/or the time trend. The model is exible enough to allow the number of breaks and their position to differ across individuals. The test is shown to have an exact limit distribution with a good nite sample performance. Its application to a typical panel data set of real per capita GDP gives support to the trend stationarity of these series.stationarity test, multiple structural changes, gdp per capita, panel data

Level shifts in a panel data based unit root test. An application to the rate of unemployment

Several unit root tests in panel data have recently been proposed. The test developed by Harris and Tzavalis (1999 JoE) performs particularly well when the time dimension is moderate in relation to the cross-section dimension. However, in common with the traditional tests designed for the unidimensional case, it was found to perform poorly when there is a structural break in the time series under the alternative. Here we derive the asymptotic distribution of the test allowing for a shift in the mean, and assess the small sample performance. We apply this new test to show how the hypothesis of (perfect) hysteresis in Spanish unemployment is rejected in favour of the alternative of the natural unemployment rate, when the possibility of a change in the latter is considered.

Fractal Photonic Crystal Waveguides

We propose a new class of one-dimensional (1D) photonic waveguides: the fractal photonic crystal waveguides (FPCWs). These structures are photonic crystal waveguides (PCWs) etched with fratal distribution of grooves such as Cantor bars. The transmission properties of the FPCWs are investigated and compared with those of the conventional 1D PCWs. It is shown that the FPCW transmission spectrum has self-similarity properties associated with the fractal distribution of grooves. Furthermore, FPCWs exhibit sharp localized transmissions peaks that are approximately equidistant inside the photonic band gap

Single-pixel imaging of the retina through scattering media

Imaging the retina of cataractous patients is useful to detect pathologies before the cataract surgery is performed. However, for conventional ophthalmoscopes, opacifications convert the lens into a scattering medium that may greatly deteriorate the retinal image. In this paper we show, as a proof of concept, that it is possible to surpass the limitations imposed by scattering applying to both, a model and a healthy eye, a newly developed ophthalmoscope based on single-pixel imaging. To this end, an instrument was built that incorporates two imaging modalities: conventional flood illumination and single-pixel based. Images of the retina were acquired firstly in an artificial eye and later in healthy living eyes with different elements which replicate the scattering produced by cataractous lenses. Comparison between both types of imaging modalities shows that, under high levels of scattering, the single-pixel ophthalmoscope outperforms standard imaging methods

Pattern-induced anchoring transitions in nematic liquid crystals

In this paper we revisit the problem of a nematic liquid crystal in contact with patterned substrates. The substrate is modelled as a periodic array of parallel infinite grooves of well-defined cross section sculpted on a chemically homogeneous substrate which favors local homeotropic anchoring of the nematic. We consider three cases: a sawtooth, a crenellated and a sinusoidal substrate. We analyse this problem within the modified Frank-Oseen formalism. We argue that, for substrate periodicities much larger than the extrapolation length, the existence of different nematic textures with distinct far-field orientations, as well as the anchoring transitions between them, are associated with the presence of topological defects either on or close to the substrate. For the sawtooth and sinusoidal case, we observe a homeotropic to planar anchoring transition as the substrate roughness is increased. On the other hand, a homeotropic to oblique anchoring transition is observed for crenellated substrates. In this case, the anchoring phase diagram shows a complex dependence on the substrate roughness and substrate anchoring strength.Comment: 36 pages, 15 figures, revised version submitted to Journal of Physics: Condensed Matte

Towards an analytical framework for tailoring supercontinuum generation

A fully analytical toolbox for supercontinuum generation relying on scenarios without pulse splitting is presented. Furthermore, starting from the new insights provided by this formalism about the physical nature of direct and cascaded dispersive wave emission, a unified description of this radiation in both normal and anomalous dispersion regimes is derived. Previously unidentified physics of broadband spectra reported in earlier works is successfully explained on this basis. Finally, a foundry-compatible few-millimeters-long silicon waveguide allowing octave-spanning supercontinuum generation pumped at telecom wavelengths in the normal dispersion regime is designed, hence showcasing the potential of this new analytical approach

Estudio comparativo de las versiones más recientes de HTTP

[ES] En este trabajo estudiaremos las características que introducen las últimas versiones del Protocolo de Transferencia de Hipertexto (HTTP) para mejorar las prestaciones de su predecesor, HTTP/1.1. En primer lugar analizaremos las ventajas que introducen HTTP/2 y HTTP/3, así como los desafíos con los que cuenta cada versión y veremos el nivel de despliegue actual de ambas tecnologías en Internet. A continuación, repasaremos el intercambio de mensajes para poder contemplar las mejoras que introducen estas dos últimas versiones. Por último, plantearemos tres escenarios, para analizar cómo se comporta cada una de las versiones ante distintas simulaciones en la configuración del enlace y para evaluar el comportamiento real en sitios web que hacen uso de ambas versiones.[EN] In this work we will study the features introduced by the latest versions of the Hypertext Transfer Protocol (HTTP) in order to improve the performance of its predecessor, HTTP/1.1. First, we will analyze the advantages that HTTP/2 and HTTP/3 introduce, as well as the challenges that each version has to face, and we will see the current level of deployment of both technologies on the Internet. Next, we will review the exchange of messages to be able to contemplate the improvements that these last two versions introduce. Finally, we will propose three scenarios, to analyze how each of the versions behaves in the face of different simulations in the link configuration and to evaluate the real behavior on websites that use both versions.Tomás Silvestre, E. (2021). Estudio comparativo de las versiones más recientes de HTTP. Universitat Politècnica de València. http://hdl.handle.net/10251/172835TFG

Displasia Epiphysalis Capitis Femoris : (Displasia de Meyer)

Se presentan 13 casos de Displasia Epifisaria de la cabeza femoral analizando los problemas diagnósticos con otras patologías y especialmente con la enfermedad de Perthes. Se discute su posible patogenia de probable origen vascular dada la relación entre ambos procesos.The authors report thirteen cases of displasia epiphysialis capitis femoris analyzing its differential diagnosis 'with other pathologies, especially with Perthes' disease. They argue about its pathogenesis of probably vascular origin, and the relation among these two entities